This invention relates to improvements in an ink jet printer adapted to eject ink droplets against a recording medium for recording an information thereon in accordance with video signals. More particularly, it relates to a deflection electrode assembly for use in a multi-nozzle ink jet printer having a plurality of nozzles for high speed printing to control the direction of travel of ejected ink droplets under an electric field.
Systems for controlling the direction of travel of ejected ink droplets under an electric field can be grouped into two categories. A first type has nozzles equal in number to the number of the image units for each line and the deflection electric field is applied perpendicular to the nozzle array. A second type has nozzles in a lesser number than that of the image units for each line and the deflection electric field is applied in the direction parallel to the nozzle array. This invention is more specifically concerned with the second type deflection electrode unit. It is important with the deflection electric field that the intensity of the electric field be set uniformly over all of the nozzles and that the deflection electrode be kept free from dust.
Plate-shaped electrodes have been used as deflection electrodes for controlling the direction of travel of ink droplets, but it has been found that they have the tendency to be soiled with ink mist existing in the injected ink droplets or generated when the injected ink droplets strike against a recording medium. Particularly where a number of electrode pairs are arranged in the same direction of the nozzle array, the distance between the adjacent electrode plates are extremely reduced and it is very difficult to produce such an electrode plate array. In addition, the distance between the electrode plates becomes irregular to cause disturbances in the generated electric field when ink sticks to and laminates on the deflection electrodes. This causes the print position to be offset on the recording medium, resulting in poor quality print as well as discharge or shorts through the laminated ink. Also, it is difficult to scrape the ink off the electrode plates without disassembling and washing them.
In the prior art a jet ink printer assembly using jet deflection by an electrical field is disclosed in Japanese Utility Model Laid-Open publication No. 47-21628. In that prior art system a plurality of jet ink nozzles are aligned on a support member. An accelerating electrode is interposed between the nozzles and the electrical deflection apparatus. A voltage is applied between the nozzles and the accelerating electrode to cause the release pattern to be a fine stream of charged particles. Deflection of the stream by the deflection apparatus causes the jets to impact the recording medium in the desired printing orientation. A conductor is arranged at ends of the nozzle support member to adjust the applied voltage and therefore the electric field between the nozzles and the accelerating electrode.